The development of a cryogenic optical delay line for DARWIN

TNO, in cooperation with Micromega-Dynamics, SRON, Dutch Space and CSL, has designed a compact breadboard cryogenic delay line for use in future space interferometry missions. The work is performed under ESA contract in preparation for the DARWIN mission. The breadboard (BB) delay line is representative of a future flight mechanism, with all materials and processes used being flight representative. In order to enable single stage OPD actuation, the delay line needs to have: • low moving mass; • low friction variations (e.g. stick/slip, bearing noise, power and signal wire torques); • low hysteresis; • linear behaviour. An extensive trade off study has been performed to select the best concept for the DARWIN ODL [2]. TNO applies a minimum-number-of-stages philosophy to all delay lines it develops. A smaller number of actuation stages simplifies the OPD control algorithm The selected concept has a single stage voice coil actuator for Optical Path Difference (OPD) control, driving a two mirror cat’s eye. Five magnetic bearings constrain 5 degrees of freedom (the OPD controller constrains the other degree of freedom) and provide frictionless and wear free operation with zero-hysteresis